The present invention relates to a vacuum circuit interrupter and, in particular, relates to a vacuum circuit interrupter and a method of manufacturing the same which are suitable for improving its vacuum tightness and production efficiency.
A vacuum circuit interrupter is an important element in a vacuum circuit breaker, and is composed by a vacuum vessel constituted by sealing both ends of a hollow cylindrical insulation body with metal end plates and a pair of separable electrodes constituted by a stationary conductor and a movable conductor disposed in the vacuum vessel. One of the electrodes is connected to the stationary conductor and the other end of the stationary conductor extends in vacuum tightness through the metal end plate. The other electrode is secured to one end of the movable conductor and the movable conductor is connected in vacuum tightness to the other metal end plate via a bellows.
Further, copper was used for the stationary and movable conductors and, since the joining portions with the hollow cylindrical insulation body of the metal end plates are subjected to many stresses and, in particular, by heating stress, a material such as phosphorus deoxidized copper, Fe--Ni alloy and Fe--Ni--Co alloy has been used for the metal end plates as disclosed in JP-A-5-41143(1993).
The above mentioned parts constituting the vacuum circuit interrupter are joined by brazing which makes use of a brazing metal as a joining member.
The brazing is performed in such a manner that a brazing material is placed between or near the members to be joined, and is heated at higher than the melting point of the brazing material in a furnace of non-oxidizing atmosphere such as a vacuum furnace or hydrogen furnace to melt the brazing material to thereby join the members. Further, TIG welding and plasma welding can be used for joining the parts constituting the vacuum circuit interrupter.
During production of a vacuum circuit interrupter, evacuation and brazing are performed at the same time in a vacuum furnace and the inside of the vacuum circuit interrupter is evacuated and vacuum sealed. For example, such a method is disclosed in JP-A-59-175521(1984) in which after partially assembling the parts the assembly is sealed in vacuum tightness in a vacuum furnace.
More specifically, both a stationary electrode, a stationary conductor and a stationary side metal end plate, and a movable electrode, a movable conductor, a metallic bellows and a movable side metal end plate, are first joined by brazing. Subsequently, the stationary side metal end plate and the movable side metal end plate are joined by brazing in a vacuum furnace to the hollow cylindrical insulation body in such a manner that the stationary side metal end plate and the movable side metal end plate sandwich the hollow cylindrical insulation body. After completing the brazing operation, silver plating is applied on the respective external connection terminal portions of the stationary and movable conductors.
Further, many investigations have been performed for improving vacuum sealing of the vacuum circuit interrupter. JP-B-5-31245(1993) discloses one such investigation in which an improvement of the brazing material for the joining member is proposed, and JP-A-2-195618(1990) discloses another investigation in which, in order to properly guide parts to be sealed, a ring shaped brazing member having a plurality of non-continuous projections along both inner and outer circumferences thereof is used.
For the purpose of vacuum sealing the inside of the vacuum circuit interrupter, if the parts are joined through a single brazing operation, no sufficient heat is transmitted through the single brazing operation for joining both the stationary conductor and the stationary electrode, and the movable conductor and the movable electrode; thereby reliable brazing cannot be obtained. For this reason, the joining method as explained above was used in which both the stationary electrode, the stationary conductor and the stationary side metal end plate, and the movable electrode, the movable conductor, the metallic bellows and the movable side metal end plate, are first joined by brazing, and subsequently, the stationary side metal end plate and the movable side metal end plate are joined by brazing in a vacuum furnace to the hollow cylindrical insulation body. With such a method it is found out that the brazing operation time is prolonged which decreases production efficiency (work efficiency) and increases the production cost of such vacuum circuit interrupters.
Further, when silver plating is applied to the connecting portions with the external conductors of the stationary and movable conductors after the brazing operation between the parts, a solvent such as acid and a plating electrolyte are coated on the surface of the connecting portions. However, these materials show a corrosive property such that when these corrosive materials remain at the vacuum circuit interrupter, a significant problem such as vacuum leakage and the like is caused. Therefore the corrosive materials have to be completely removed which requires substantial time and further reduces production efficiency (work efficiency) and increases production cost of the vacuum circuit interrupter. Further, when joining the parts constituting the vacuum circuit interrupter in the vacuum furnace, heat is supplied through radiation to the vacuum circuit interrupter so as to melt the brazing material of the joint member; however, copper, which is a major constituent material, is likely to reflect the radiation heat and absorbs a limited amount of heat so that it takes time for heating the vacuum circuit interrupter and prevents a uniform reditation heat transmission, causing a non-uniform melting of the brazing material of the joining member which induces vacuum leakage.
Further, in the conventional vacuum circuit interrupter as indicated above, since a material such as Fe--Ni alloy and Fe--Ni--Co alloy different from the conductor material Cu was used for the metal end plates and further, many constituent parts were required, joint portions which require a vacuum-tight seal expand, which also induces vacuum leakage.
Further, although with the conventional method, such as one using an improved brazing material of a joint member or guiding members by a plurality of projections formed on the joint member, the vacuum-tight sealing property of the vacuum circuit interrupter is improved; however, no vacuum circuit interrupters having a reliable vacuum-tight sealing structure have been obtained until now. Accordingly, the vacuum-tight sealing properties of the conventional vacuum circuit interrupters are still insufficient.